Personally, we've never wandered through a nursery we didn't like, but Mesquite Valley Growers is the biggest and best-stocked place in town. They have everything: Plants for water gardens and a zillion more for xeriscapes, begonias and ironwoods, turf and orchids. Pots. Heirloom seeds. Spigots with handles shaped like frogs. Help is knowledgeable, friendly and easy to find. They hold free classes and demonstrations and do really endearing things like offer comparison tastings (in season) of the fruit of the citrus varieties they sell. The place hums, so try to hold on and not get tractor-beamed into MVG on the first pretty Saturday of fall. But if you do, you won't have to watch for the sign: Just turn where everyone else does.
Runners up:
2. Desert Survivors Plant Nursery, 1020 W. Starr Pass Road, 791-9309
3. Harlow Gardens, 5620 E. Pima St., 886-5475